Crist Amelynck

An ecosystem-scale perspective of the net land methanol flux: synthesis of micrometeorological flux measurements

Methanol is the second most abundant volatile organic compound in the troposphere and plays a significant role in atmospheric chemistry. While there is consensus about the dominant role of living plants as the major source and the reaction with OH as the major sink of methanol, global methanol budgets diverge considerably in terms of source/sink estimates reflecting uncertainties in the approaches used to model, and the empirical data used to separately constrain these terms. Here we compiled micrometeorological methanol flux data from eight different study sites and reviewed the corresponding literature in order to provide a first cross-site synthesis of the terrestrial ecosystem-scale methanol exchange and present an independent data-driven view of the land–atmosphere methanol exchange. Our study shows that the controls of plant growth on the production, and thus the methanol emission magnitude, and stomatal conductance on the hourly methanol emission variability, established at the leaf level, hold across sites at the ecosystem-level. Unequivocal evidence for bi-directional methanol exchange at the ecosystem scale is presented. Deposition, which at some sites even exceeds methanol emissions, represents an emerging feature of ecosystem-scale measurements and is likely related to environmental factors favouring the formation of surface wetness. Methanol may adsorb to or dissolve in this surface water and eventually be chemically or biologically removed from it. Management activities in agriculture and forestry are shown to increase local methanol emission by orders of magnitude; they are however neglected at present in global budgets. While contemporary net land methanol budgets are overall consistent with the grand mean of the micrometeorological methanol flux measurements, we caution that the present approach of simulating methanol emission and deposition separately is prone to opposing systematic errors and does not allow taking full advantage of the rich information content of micrometeorological flux measurements.

Gas phase reactions of CF3O− and CF3O−H2O with nitric, formic, and acetic acid

Abstract The reactions of CF 3 O − , CF 3 O − H 2 O and CF 3 O − HF with HNO 3 , HCOOH, and CH 3 COOH have been studied at room temperature in a flowing afterglow instrument. Apart from the reaction of CF 3 O − HF with CH 3 COOH, all reactions proceed at the collision rate. Bare CF 3 O − ions react with the three acids mainly by fluoride transfer. An unambiguous identification of the reaction mechanisms of CF 3 O − H 2 O and CF 3 O − HF with the three neutral reactants is difficult to assess. The possibility to perform in situ measurements of HNO 3 , HCOOH, and CH 3 COOH concentrations in the atmosphere by chemical ionization mass spectrometry (CIMS), using a CF 3 O − ion source will be discussed.

Stratospheric chemical ionization mass spectrometry: nitric acid detection by different ion molecule reaction schemes

Abstract Detailed height profiles of stratospheric nitric acid mixing ratios have been derived with a baloon borne chemical ionization mass spectrometer by applying several ion molecule reaction schemes, each associated to a specific and selective ion source. These ions (CO 3 − , Cl n − , CF 3 O − , and CF 3 O − H 2 O) give rise to specific product ions (mainly CO 3 − HNO 3 , NO 3 − HCl, NO 3 − HF, and CF 3 O − HNO 3 ) upon reaction with ambient nitric acid molecules. This paper reports on the instrumental details as well as on the results obtained during two balloon flights with the instrument. Within the accuracy of the measurements, the nitric acid height profiles obtained with the three different ion sources are in good agreement with one another as well as with literature data.

Emissions of biogenic volatile organic compounds from Fraxinus excelsior and Quercus robur under ambient conditions in Flanders (Belgium)

A dynamic branch enclosure system was used to measure emission rates of biogenic volatile organic compounds (BVOCs) from two common European tree species: Fraxinus excelsior and Quercus robur under ambient conditions in Flanders (Belgium). Both tree species were studied for seasonal variability of BVOC emission rates under natural biotic stress (infestations). Emissions were normalized at standard conditions of temperature and photosynthetic active radiation (PAR) (30°C and 1000 µmol m−2 s−1, respectively). Emission rates from Fraxinus excelsior were highest in May (9.56 µg gDW −1 h−1) and lowest in October (1.17 µg gDW −1 h−1). This tree species emitted (Z)-β-ocimene, (E)-β-ocimene and α-farnesene during the entire measurement period and additionally isoprene only in May. Quercus robur showed isoprene emission variations according to the seasonal cycle with rates of 30, 106 and 29 µg gDW −1 h−1 in May, August and October, respectively. Apart from isoprene, (E)-β-ocimene and β-caryophyllene were emitted through the entire experimental period.

GAS PHASE REACTIONS OF HNO3 WITH CL-, CL-H2O, AND CL-HCL, OF CL2 WITH CL-H2O AND CL-HCL, AND OF HCL WITH CL-H2O

Abstract This paper reports on the gas phase reactions of HNO 3 with Cl − , Cl − H 2 O, and Cl − HCl, of Cl 2 with Cl − H 2 O and Cl − HCl, and of HCl with Cl − H 2 O. Rate constants and product ions have been determined at room temperature and at low pressures (0.7–1.7 mb) by means of a flow tube reactor coupled to a quadrupole mass spectrometer. Apart from Cl − HCl + Cl 2 , all reactions proceed at the collision rate. The reaction mechanism for all reactions, except for Cl − + HNO 3 , seems to be ligand switching. The implication of the results on a chemical ionisation method for the in situ derivation of stratospheric nitric acid concentrations is discussed.

Long-term measurements of chlorophyll a fluorescence using the JIP-test show that combined abiotic stresses influence the photosynthetic performance of the perennial ryegrass ( Lolium perenne ) in a managed temperate grassland

Several experiments have highlighted the complexity of stress interactions involved in plant response. The impact in field conditions of combined environmental constraints on the mechanisms involved in plant photosynthetic response, however, remains understudied. In a long-term field study performed in a managed grassland, we investigated the photosynthetic apparatus response of the perennial ryegrass (Lolium perenne L.) to environmental constraints and its ability to recover and acclimatize. Frequent field measurements of chlorophyll a fluorescence (ChlF) were made in order to determine the photosynthetic performance response of a population of L. perenne. Strong midday declines in the maximum quantum yield of primary photochemistry (FV FM ) were observed in summer, when a combination of heat and high light intensity increased photosynthetic inhibition. During this period, increase in photosystem I (PSI) activity efficiency was also recorded, suggesting an increase in the photochemical pathway for de-excitation in summer. Strong climatic events (e.g. heat waves) were shown to reduce electron transport between photosystem II (PSII) and PSI. This reduction might have preserved the PSI from photo-oxidation. Periods of low soil moisture and high levels of sun irradiance increased PSII sensitivity to heat stress, suggesting increased susceptibility to combined environmental constraints. Despite the multiple inhibitions of photosynthetic functionality in summer, the L. perenne population showed increased PSII tolerance to environmental stresses in August. This might have been a response to earlier environmental constraints. It could also be linked to the selection and/or emergence of well-adapted individuals.

SIFT Ion Chemistry Studies Underpinning the Measurement of Volatile Organic Compound Emissions by Vegetation

Chemical Ionization Mass Spectrometry (CI-MS) techniques are appropriate for the determination of volatile organic compound (VOC) emissions from terrestrial vegetation, provided that these compounds have unique analytical ions. In practice, however, many plant volatiles, and mainly those emitted by the isoprenoid and lipoxygenase biochemical pathways, have CI product ions at overlapping m/z values. In this paper, Selected Ion Flow Tube (SIFT) gas phase ion chemistry studies of several series of plant volatile classes using H3O+ and NO+ reagent ions, which have provided the kinetic and mechanistic parameters required for plant volatile quantification by SIFT-MS, are reviewed. The available information has been gathered into tables which allow the reader to decide which analytical ions are best monitored to quantify specific biogenic VOC emissions by SIFT-MS in the presence of interfering compounds. Some typical examples of interferences and how they can be resolved are subsequently given. The reviewed ion chemistry, obtained under SIFT conditions, is also relevant to the analysis of biogenic VOC emissions by Proton Transfer Reaction - Mass Spectrometry (PTR-MS).

Gas phase reactions of negative ions with ClONO2

Abstract The reactions of the halide anions (F − , Cl − , Br − , and I − ), NO 2 − , SF 6 − , CO 3 − and CO 4 − with ClONO 2 have been studied at room temperature in a flowing afterglow apparatus. All these reactions are found to proceed at the collision limit and the experimental data are compared with literature values. The reaction of I − with ClONO 2 was studied at stratospheric pressures and temperatures in view of its use as a possible precursor ion for the measurement of stratospheric N 2 O 5 +ClONO 2 mixing ratio height profiles by chemical ionization mass spectrometry. No pressure or temperature dependence of the rate constant has been observed. In order to correct the observed rate constants for HNO 3 impurities, the reaction rate constants of F − , Br − , and NO 2 − with HNO 3 have also been determined. In addition, the apparent second-order clustering rate constant of NO 3 − with ClONO 2 in Ar/N 2 and Ar/He mixtures has been measured.

Chemical ionization by [NO]+ and subsequent collision‐induced dissociation for the selective on‐line detection of monoterpenes and linalool

Existing on-line Chemical Ionization Mass Spectrometry (CIMS) techniques for quantification of atmospheric trace gases, such as Biogenic Volatile Organic Compounds (BVOCs), suffer from difficulty in discriminating between isomeric (and more generally isobaric) compounds. Selective detection of these compounds, however, is important because they can affect atmospheric chemistry in different ways, depending on their chemical structure. In this work, Flowing Afterglow Tandem Mass Spectrometry (FATMS) was used to investigate the feasibility of the selective detection of a series of monoterpenes, an oxygenated monoterpene (linalool) and a sesquiterpene (β-caryophyllene). Ions at m/z 137 from [H(3)O](+) chemical ionization of α-pinene, linalool and β-caryophyllene have been subjected to Collision-Induced Dissociation (CID) with Ar in the collision cell of a tandem mass spectrometer at center-of-mass energies ranging between 0 and 8 eV. Similar fragmentation patterns were obtained, demonstrating that this method is not suited for the selective detection of these compounds. However, CID of the ions at m/z 136 produced via [NO](+) chemical ionization of a series of monoterpenes has revealed promising results. Some tracer-product ions for individual compounds or groups of compounds were found, which can be considered as a step forward towards selective on-line monitoring of BVOCs with CIMS techniques.

Reactions of CF3O− core ions with ClONO2 and H2O

The reactions of CF3O−, CF3OHF− and CF3OH2O− with ClONO2 have been studied in the temperature range 225–325 K. The reactions of CF3O− and CF3OH2O− with ClONO2 proceed at the collision rate whereas the reaction of CF3OHF− with ClONO2 is slower. No significant temperature dependence of the rate constant has been found for each reaction. The mechanistic study has shown that the reaction of CF3O− with ClONO2 proceeds by fluoride transfer and the product of the reaction between CF3OH2O− and ClONO2 is the cluster ion CF3OClONO2−. The equilibrium reaction of CF3O− with H2O has been also studied between 262 and 295 K. Values of − 63.2 ± 6.7 kJ mol−1 and − 114.6 ± 23.9 J mol−1 K−1 were derived for the standard reaction enthalpy and entropy, respectively.